In recent years, there has been widespread use of digital contents including a picture, music, a video, and the like, to be stored for use in a large-capacity storage such as hard disk drive. This has led to a growing demand for, among others, a search technique to retrieve a desired content from a great number of contents, and a technique to automatically categorize and organize contents, giving rise to development of techniques in these fields.
In the music field, there has been disclosed a device configured to create playlists of collections of pieces of music fitting to a user's desired impression. There have been patent literatures 1 and 2 describing a delivery system including a terminal configured to create playlists, and a server also configured to create playlists for transmission to the terminal for use. This permits a listening of pieces of music fitting to a user's impression from among a large music database on the server.
In these conventional techniques, there has been use of a coordinate system for creation of playlists, representing subjective impressions of pieces of music (audio information) such as “cheerful”, “gloomy”, “aggressive”, and “soft”, permitting a creation of playlist fitting to a user's impression without the need of previous knowledge about the pieces of music. This also permits a playlist with a combination of pieces of music having different impressions, thus allowing for a creation of playlist full of variety.    Patent document 1: Japanese Patent Application Laid-Open Publication No. 2003-15666    Patent document 2: Japanese Patent Application Laid-Open Publication No. 2004-117632